For last few years, multistage acid fracture treatments have become a common practice to develop the carbonate gas reservoirs in Saudi Arabia. Different multistage completions systems have been used in more than 50 wells that were acid fractured anywhere from 2 to 6 stages per lateral. These systems include multistage fracturing (MSF) with openhole frac sleeves in combination with open hole hydraulic or swellable packers to provide zonal isolation between fracture stages. This paper provides an analysis of the effectiveness of these fracturing treatments comparing the pre-and post-frac gas production rates of the wells as functions of fracture half-length, conductivity, and some of the main reservoir properties such as porosity and flow capacity.One major concern from the open hole MSF treatments is the zonal isolation provided by the open hole packer assemblies. This is very important to ensure fracture containment for the zone the induced fracture is intended for. Failure in isolation can lead to communications between intervals allowing the pumped frac stage to propagate to the previously opened frac stage. This could result in fracturing less number of stages than designed. Consequently, the expected production rate may not be achieved. This study also analyzes the post-frac pressure build up response for selected carbonate reservoir wells to compute number of effective fractures created during the treatment. The reason of isolation failures and how to avoid that in the future MSF treatments are discussed in this paper. Several field data including post-frac production data have been analyzed for MSF acid fracturing in the carbonate gas reservoirs to establish the treatment effectiveness. This analysis will be useful to optimize the future well stimulation programs and improve gas production.
The clastic non-associated gas reservoirs are encountered in one of the Saudi Arabian oilfields. There is a wide variation in permeability in this Devonian age formation, varying from tight rocks with 0.1 md or less to more than few Darcie's in highly unconsolidated sandstones. While the prolific areas are easily producible at sustained high gas rates by conventional drilling and using sand control completion mechanisms, the relatively tighter areas require hydraulic fracturing to sustain commercial flow rate. During the last 10 years, the field A focused on exploiting gas reservoirs is being developed with vertical or S-shaped wells, and completed using a monobore tubular assembly. Proppant fracturing treatments are routinely conducted in multiple stages along the vertical wellbore. Fracture treatment parameters are adjusted over time by the introduction of different fracture fluids to enhance stability and avoid premature screen out. Proppant flow back measures were taken with the use of resin-coated proppants. A large database was developed on stimulation treatments and results that allowed conducting a detailed analysis to understand the behavior and effect of hydraulic fracturing trends on the reservoir performance to optimize the design parameters and further increase reservoir potential. This paper documents the analysis of the pre- and post-fracture treatment data, production analysis and thorough evaluation of petrophysical and geomechanical measurements from this massive database of 10-year long operational period. This study shows that there is a room to improve fracturing treatments and fluid chemistry and recommends a step change in the well stimulation strategy by modifying some existing technologies and also applying novel technologies that have been carefully studied and approved using laboratory and field trial testing. The results from the application of this new strategy are presented in the paper using actual examples.
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